The present invention pertains to compositions containing, on the one hand, copolymers of ethylene and alpha-olefin(s) and, on the other hand, copolymers of ethylene and polar comonomer(2) in which at least one of the copolymers is modified by means of a suitable chemical agent.
The copolymers of ethylene and at least one alpha-olefin have been known for many years and have undergone a noteworthy development such that the more recent the development, the lower is their density. They are generally known under the name of "low-density linear polyethylene" if their density is between circa 0.915 and 0.945, under the name of "very-low-density linear polyethylene" if their density is between circa 0.890 and circa 0.915, and under the name of "ultra-low-density linear polyethylene" if their density is between circa 0.850 and circa 0.890.
It is known that the density and the degree of crystallinity of the copolymer decrease as the alpha-olefin(s) content increases. This is accompanied for the copolymer by an increasingly pronounced elastomeric behavior with correlatively decreasing thermoplastic characteristics.
The copolymers of ethylene and at least one alpha-olefin that have a very low density or, to an even greater extent, those with an ultra-low density are therefore suitable for use in applications which had previously been reserved for completely amorphous elastomers such as the ethylene and propylene rubbers known under the name EPR and the ethylene, propylene and diene rubbers known under the name EPDM.
In the context of the research that resulted in the present invention, it was particularly envisioned to effect the transformation of very-low- or ultra-low-density copolymers of ethylene and at least one alpha-olefin into wear-intensive pieces (industrial articles with good resistance to abrasion) such as shoe soles, paving slabs, and pipes for transporting abrasive products. It was discovered that it was not possible for a copolymer of given density to simultaneously obtain good resistance to abrasion and good alternating bending performance. Thus, the very-low-density linear polyethylenes have good abrasion resistance but no alternating bending performance (they break after several hundred cycles). Most of the ultra-low-density linear polyethylenes have better alternating bending performance, although it is insufficient for certain applications, but poor resistance to abrasion.
Thus, the problem to be resolved by the present invention is the development of a modification of low-density or ultra-low-density copolymers of ethylene and alpha-olefin(s) which makes it possible to obtain industrial articles that simultaneously have good resistance to abrasion and good alternating bending performance (preferably at least 100,000 bendings). This problem is resolved by the present invention which will now be presented in detail.